(a) Technical Field
The present invention relates to a polypropylene resin composition having superior mechanical properties. More particularly, the present invention relates to a polypropylene resin composition, which exhibits no cracking even when exposed to aromatic compounds or various other chemicals because of its superior chemical resistance, is easily processable because of its excellent mechanical properties such as impact strength, rigidity, etc., and is useful for use in automotive interior parts because of its superior scratch resistance, molding shrinkage, etc.
(b) Background Art
Among various resin compositions, acrylonitrile butadiene styrene (ABS) resin is mainly used in various electric/electronic products, automotive interior parts, etc. The ABS resin is an amorphous, milky-white, semi-transparent plastic material formed by copolymerizing acrylonitrile (AN), butadiene and styrene. The ABS resin is also widely used for household goods, office equipment, electronic products and automotive surface parts because it is easily colored, has good surface gloss and superior mechanical properties, such as impact resistance, rigidity and scratch resistance.
However, when the ABS resin is used in indoor household goods or automotive interior parts, cracks and breakage tend to occur upon exposure to aromatic compounds and various chemicals. This is because the amorphous resin has weak chemical resistance.
A polyolefin-based thermoplastic resin, particularly a polypropylene resin, is thus often used as an alternative in these situations.
However, since the polypropylene resin is semicrystalline and has no polar or reactive group, it cannot form a strong polar bond or a hydrogen bond with polar molecules present in an interior part and, as a result, coloring becomes difficult. In addition, the polypropylene resin tends to have poor scratch resistance as impact strength is enhanced. Polypropylene resin further exhibits a higher molding shrinkage than the ABS resin, and thus a special mold is necessary when using the polypropylene resin.
As an existing polypropylene resin composition, Korean Patent No. 857,185 describes a resin composition including 50-95 parts by weight of a polypropylene resin, 5-40 parts by weight of an inorganic fiber, 0-15 parts by weight of an inorganic filler, 0-15 parts by weight of a thermoplastic rubber elastomer and a compatibilizer. The patent describes use of glass fiber as the inorganic fiber and use of talc, etc. as the filler.
U.S. Pat. No. 5,965,654 describes a resin composition and an automotive molded article including 53-68 parts by weight of a block copolymer containing a polypropylene section and a propylene-ethylene random copolymer section, 22-30 parts by weight of talc and 12-20 parts by weight of ethylene-1-butene copolymer rubber, and further including additional components such as glass fiber.
Korean Patent Application Publication No. 2006-104110 describes a polypropylene resin composition including 40-65 wt % of an ultrahigh crystalline olefin-based resin having an isotactic pentad fraction of 96% or more, 2-5 wt % of glass fiber, 5-30 wt % of talc, 5-25 wt % of a polyolefin-based elastomer and 2-4 wt % of an aluminum pigment.
European Patent No. 437,096 describes a resin composition including 45-88 wt % of a crystalline ethylene-propylene copolymer, 2-25 wt % of an inorganic filler and 10-35 wt % of a thermoplastic elastomer (ethylene-butene rubber). Korean Patent No. 804,823 describes a thermoplastic resin composition including 1-90 wt % of a polypropylene resin, 3-50 wt % of a thermoplastic elastomer, 5-50 wt % of an inorganic filler and 0.1-10 wt % of a deodorizing agent having a porous nanoball structure.
However, since these existing polypropylene resin compositions are used in applications where only mechanical rigidity is required, they are limited in providing a high quality appearance or scratch resistance as well as general physical properties or dimensional stability that is required for, e.g., automotive interior parts requiring a high quality appearance.
For these reasons, improvements in the coloring property, scratch resistance and molding shrinkage, as well as chemical resistance, impact resistance, rigidity, etc. of a polypropylene resin is necessary when such a resin is used as a material in various electric/electronic products, indoor goods and automotive interior parts.
Throughout the specification, a number of publications and patent documents are referred to and cited. The disclosure of the cited publications and patent documents is incorporated herein by reference in its entirety to more clearly describe the state of the related art and the present invention.